Method and apparatus for three-dimensional additive manufacturing with a high energy high power ultrafast laser

ABSTRACT

Methods and systems for three-dimensional additive manufacturing of samples are disclosed, including generating electromagnetic radiation from an ultrashort pulse laser, wherein the electromagnetic radiation comprises a wavelength, a pulse repetition rate, a pulse width, a pulse energy, and an average power; focusing the electromagnetic radiation into a focal region; using a powder delivery system comprising a powder vessel, a roller, and a receptacle to deposit one or more powders from the powder vessel into a receptacle at the focal region of the electromagnetic radiation and to spread the one or more powders in the receptacle into a fabrication powder bed; and using a computer to adjust the micro and macro pulses, macro pulse repetition rate, and the average power of the ultrashort pulse laser. The samples may be made with micron and/or submicron level precision and/or feature size and may be made using high temperature materials. Other embodiments are described and claimed.

I. CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 14/324,066, titled “Method and Apparatus forThree-Dimensional Additive Manufacturing with a High Energy High PowerUltrafast Laser” filed Jul. 3, 2014, which is a continuation-in-part ofU.S. patent application Ser. No. 14/287,994, titled “Method andApparatus for Three-Dimensional Additive Manufacturing with a HighEnergy High Power Ultrafast Laser,” filed May 27, 2014. All the contentsof which are hereby incorporated by reference.

II. BACKGROUND

The invention relates generally to the field of three-dimensionaladditive manufacturing. More particularly, the invention relates to amethod and apparatus for additive manufacturing of materials (metals,ceramics, glasses, semiconductors) with a high energy, high powerultrafast laser.

III. SUMMARY

In one respect, disclosed is an apparatus for three-dimensional additivemanufacturing comprising: an ultrashort pulse laser, wherein theultrashort pulse laser generates an electromagnetic radiation, whereinthe electromagnetic radiation comprises a wavelength, a pulse repetitionrate, a pulse width, a pulse energy, and an average power; a focusingmechanism comprising a focus range, and wherein the focusing mechanismis configured to focus the electromagnetic radiation into a focalregion; a powder delivery system, wherein the powder delivery systemcomprises: a powder vessel; a roller; and a receptacle; wherein thepowder delivery system is configured to deposit one or more powders intothe receptacle at the focal region of the electromagnetic radiation;wherein the powder vessel is configured to hold the one or more powders;and wherein the roller is configured to spread the one or more powdersin the receptacle into a fabrication powder bed; and a computer coupledto the ultrashort pulse laser, wherein the computer is configured toadjust the pulse repetition rate, adjust the average power of theultrashort pulse laser, and coordinate the focusing mechanism, powderdelivery system, and the one or more stages. The computer can also beused to convert the AutoCAD or SolidWorks file of the sample into 3Dprinting procedures and contours to make layer-by-layer printing ofpredefined shapes or devices.

In another respect, disclosed is a method for three-dimensional additivemanufacturing comprising: generating electromagnetic radiation from anultrashort pulse laser, wherein the electromagnetic radiation comprisesa wavelength, a pulse repetition rate, a pulse width, a pulse energy,and an average power; focusing the electromagnetic radiation into afocal region; using a powder delivery system comprising a powder vessel,a roller, and a receptacle to deposit one or more powders from thepowder vessel into a receptacle at the focal region of theelectromagnetic radiation and to spread the one or more powders in thereceptacle into a fabrication powder bed; using one or more stages toposition a sample within the scanning and focus range of theelectromagnetic radiation; and using a computer to adjust the pulserepetition rate, adjust the average power of the ultrashort pulse laser,and coordinate the focusing mechanism, powder delivery system, and theone or more stages. The method may further comprise using the computeror another computer to convert the AutoCAD or SolidWorks file of thesample into 3D printing procedures and contours to make layer-by-layerprinting of predefined shapes or devices.

Numerous additional embodiments are also possible.

IV. BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention may become apparent uponreading the detailed description and upon reference to the accompanyingdrawings.

FIG. 1 is a block diagram showing the different processes involved inthe bonding of material during additive manufacturing with differentlaser sources, in accordance with some embodiments.

FIG. 2 is a graph of the heat diffusion length versus pulse duration, inaccordance with some embodiments.

FIG. 3A is a graph of the finite-difference model of temperature versusexposure for various pulse repetition rates. FIG. 3B is a graph oflattice temperature of fs laser process at different fluence of singlepulse.

FIG. 4 is a graph of the material process mechanisms for pulsed lasers,in accordance with some embodiments.

FIG. 5 is a schematic illustration of an apparatus for additivemanufacturing with a high energy high power ultrafast laser, inaccordance with some embodiments.

FIG. 6 is an illustration of pulse shaping to form micro pulses andmacro pulses, in accordance with some embodiments.

FIG. 7 is an illustration of beam shaping a Gaussian beam to a square orround flat top, in accordance with some embodiments.

FIG. 8A is a schematic illustration of a powder delivery system for anapparatus for additive manufacturing by selective laser melting with ahigh energy high power ultrafast laser and FIG. 8B is a close-up of themelting of the powder of the fabrication powder bed, in accordance withsome embodiments.

FIG. 9 is an SEM of a formed shaped structure resulting from selectivelaser melting of tungsten powder, in accordance with some embodiments.

FIG. 10 is an SEM of the cross-section of the formed shaped structureresulting from selective laser melting of tungsten powder, in accordancewith some embodiments.

FIG. 11 is an EDX spectrum of a fully melted region of the formed shapedstructure resulting from selective laser melting of tungsten powder, inaccordance with some embodiments.

FIG. 12 is an SEM of a ceramic wire resulting from selective lasermelting of hafnium diboride (HfB₂) powder, in accordance with someembodiments.

FIG. 13 is an SEM of the cross-section of the ceramic wire resultingfrom selective laser melting of HfB₂ powder, in accordance with someembodiments.

FIG. 14 is an SEM of the grain structure of the ceramic wire resultingfrom selective laser melting of HfB₂ powder, in accordance with someembodiments.

FIG. 15 is an EDX spectrum of a fully melted region of the ceramic wireresulting from selective laser melting of HfB₂ powder, in accordancewith some embodiments.

FIG. 16 is a block diagram illustrating a method for additivemanufacturing by selective laser melting with a high energy high powerultrafast laser, in accordance with some embodiments.

While the invention is subject to various modifications and alternativeforms, specific embodiments thereof are shown by way of example in thedrawings and the accompanying detailed description. It should beunderstood, however, that the drawings and detailed description are notintended to limit the invention to the particular embodiments. Thisdisclosure is instead intended to cover all modifications, equivalents,and alternatives falling within the scope of the present invention asdefined by the appended claims.

V. DETAILED DESCRIPTION

One or more embodiments of the invention are described below. It shouldbe noted that these and any other embodiments are exemplary and areintended to be illustrative of the invention rather than limiting. Whilethe invention is widely applicable to different types of systems, it isimpossible to include all of the possible embodiments and contexts ofthe invention in this disclosure. Upon reading this disclosure, manyalternative embodiments of the present invention will be apparent topersons of ordinary skill in the art.

Additive manufacturing (AM) is gaining great interest now that manyindustrial metals like titanium and aluminum are used in established AMprocesses. However, some challenges still remain. Examples of thesechallenges are listed as follows.

One challenge is in the production of micro parts. Currently, parts witha resolution of 35 μm can be made from tungsten using continuous wave(CW) fiber laser micro sintering as reported by P. Regenfuss, R. Ebert,and H. Exner, in “Laser Micro Sintering: a Versatile Instrument for theGeneration of Microparts.” (Laser Technik Journal, Vol. 4, Issue 1,Pages 26-31, January 2007) These micro parts are being used asmicro-engines in micro-satellites to maneuver the satellites while inorbit and in micro-robots to propel the robots. Unlike bulk engines,which can be assembled by several separated components, micro-enginesare sized from millimeters to a few centimeters and thus have to be madeas a single piece with high resolution at the micron level.Additionally, since the engines are composed of various types ofmaterials (e.g. steel, nickel, titanium), complex structure, and shapes,especially irregular shapes, the use of conventional methods of scalingdown in size while keeping the desired performance and robustness (e.g.stress, tension, strength, fatigue, thermal cycling, thrust) is limited.The use of CW lasers for machining micro parts can only go so far sinceCW lasers produce a heat affected zone (HAZ) which limits the processresolution and quality, such as strength and surface roughness, ofmicro-sized parts. A post process is usually required to try toalleviate some of these shortcomings, but this in turn further limitsthe miniaturization of micro devices such as engines.

Another challenge is in the production of high temperature metal parts.To date, the majority of AM technology development has focused onconventional structural materials such as titanium and steel. The use ofAM technology to refractory metal alloy components, such as tools towork metals at high temperatures, wire filaments, rocket/airplaneengines and nozzles, casting molds, and chemical reaction vessels incorrosive environments for example, holds even greater potential todrive affordability given the high raw material costs and complexprocessing methods associated with such refractory metal alloy products.Refractory metals are a class of metals that are extraordinarilyresistant to heat and wear, are chemically inert, and have a relativelyhigh density. The expression “refractory metals” is mostly used in thecontext of materials science, metallurgy, and engineering. Even so, thedefinition of which elements belong to the “refractory metals” groupdiffers. The most common definition includes five elements: two of thefifth period (niobium and molybdenum) and three of the sixth period(tantalum, tungsten, and rhenium). Refractory metals all share someproperties, including a melting point above 2000° C. and high hardnessat room temperature. The melting points of niobium, molybdenum,tantalum, tungsten, and rhenium, are 2750° C., 2896° C., 3290° C., 3695°C., and 3459° C., respectively. As a reference, titanium and aluminumhave melting points of roughly 1,650° C. and 650° C., respectively. Thehigh melting points of refractory metals make powder metallurgycomplicated for fabricating components from these metals. CW or longpulse (>ns) mode laser processing can only heat the metals to 1500° C.normally, which is the base line of the plots shown in FIG. 3A and FIG.3B. So, for refractory metals or ceramics with melting temperatures over2000° C., CW laser additive manufacturing is a difficult or impossibleprocess.

A third challenge is in the production of ceramic parts. Ultra hightemperature ceramics (UHTCs), such as hafnium (Hf) and zirconium (Zr)based diboride (HfB₂ and ZrB₂), titanium carbide (TiC), titanium nitride(TiN), thorium dioxide (ThO₂), silicon carbide (SiC), tantalum carbide(TaC) and their associated composites, have melting temperatures of over3000° C. Thus, similar to that of refractory metals, CW or long pulse(>ns) laser AM processing is not possible for melting and bonding.

Given these challenges, methods and apparatuses are needed for resolvingeither one of the following issues or both: 1) precise AM processcontrol while concurrently reducing thermo-mechanical stresses andreducing the HAZ to achieve 3D micro-devices, such as engines, nozzles,micro-robots, and implantable devices; and 2) additive manufacturingwith high temperature materials (refractory metals and ceramics). Themethods and apparatuses of the invention described herein may solvethese shortcomings as well as others by proposing a novel method andapparatus for three-dimensional additive manufacturing by selectivelaser melting with a high energy high power ultrafast laser.

FIG. 1 is a block diagram showing the different processes involved inthe bonding of material during additive manufacturing with differentlaser sources, in accordance with some embodiments.

With CW or nanosecond (ns) lasers, the bonding of materials is a thermalprocess which necessitates that the materials to be bonded duringadditive manufacturing absorb at the CW or ns laser wavelength. For highenergy, low power ultrafast lasers, the bonding of materials is anionization process where material absorption is not necessary. Incomparison, for the novel method and apparatus for additivemanufacturing by selective laser melting with a high energy, high powerultrafast laser of this invention, the bonding of materials is both anionization process and a thermal process. Material absorption is notnecessary in either the ionization process or the thermal process foradditive manufacturing by selective laser melting with a high energy,high power ultrafast laser.

FIG. 2 is a graph of the heat diffusion length versus pulse duration, inaccordance with some embodiments.

FIG. 3A is a graph of the finite-difference model of temperature versusexposure for various pulse repetition rates. FIG. 3B is a graph oflattice temperature of fs laser process at different fluence of singlepulse.

FIG. 4 is a graph of the material process mechanisms for pulsed lasers,in accordance with some embodiments.

Femtosecond (fs) pulsed lasers have been widely used in many fieldsincluding optical waveguide writing, active photonic devices, andbonding of transparent materials. At the high peak intensity generatedby fs lasers, a wide range of materials may be ionized and joined. Themechanism of ultrashort laser pulse modification of materials involvesabsorption of fs laser energy by materials (e.g., silicon, metal, glass,and polymer) and subsequent dissipation of the absorbed energy. FIG. 2illustrates the heat diffusion length as a function of the pulseduration for a sample within a 300 K to 1500 K temperature range. As thepulse duration is shortened, the heat diffusion length is reduced, thusresulting in less HAZ.

The energy absorption process in the context of fs-laser ablationfollows the sequential steps of 1) production of initial seed electronsthrough either nonlinear photoionization of free electrons or excitationof impurity defects, 2) avalanche photoionization, and 3) plasmaformation. Note, the laser energy is only absorbed in the small focalvolume of the laser, where the intensity is high enough for multi-photonionization to occur in less than a picosecond (ps).

The energy dissipation process involves the transfer of the energy fromthe hot plasma created by laser pulses to the lattice, resulting in themodified regions in the material. This process is less well understoodthan the energy absorption process. It is known that the energydissipation process occurs on a timescale of hundreds of nanoseconds(ns) to microseconds (μs), substantially longer than the hundreds of fsrequired for the energy absorption process. It is believed that theprimary energy dissipation mechanisms are a combination of thermaldiffusion and shockwave generation, though it remains uncertain aboutwhich process is dominant and may depend on the precise writingconditions (e.g., pulse fluence, repetition rate).

For 1 kHz fs-laser systems, the time between successive pulses is on theorder of a couple milliseconds, thus allowing for any thermal energythat has been deposited by the fs-laser pulse to fully dissipate fromthe irradiated region. However, for 1 MHz or higher PRR fs-laser systemsthe time between pulses occurs at the microsecond timescale, allowingfor multiple fs-laser pulses to deposit their energy before the energycan diffuse to the surrounding lattice via thermal processes. Such aphysical process will lead to heat accumulation for local temperatureincrease (>6,000° C.), and an observably large melted volume thatextends beyond the focal volume. The difference between these two energyabsorption processes can be observed in the model illustrated in FIG. 3Aas reported by Mazur et al. (Nature Photonics, Vol. 2, 219 (2008)). Asingle pulse induced lattice temperature plot is also shown forcomparison in FIG. 3B as reported by I. H. Chowdhury and X. Xu in “Heattransfer in fs laser processing of metal.” (Numerical Heat Transfer, A44: 219-232, 2003). CW mode laser processing can only heat the metals to1500° C. normally, which is the base line of the plots. So, forrefractory metals or ceramics with melting temperatures over 2000° C.,CW laser AM process is a difficult or impossible process. The high PRRfs laser based AM is a disruptive technique.

The end results of the fs laser-material interaction are related withphysical, chemical, and mechanical changes of the material afterexposure to the laser beam. FIG. 4 summarizes the mechanisms(ionization, plasma formation, chemical reaction and recombination,phase transformation and thermal transfer, cooling, solidification, andrecrystallization) that guide the laser processing. For shorter pulsewidths, ionization is the dominant process and as pulse widths getlonger toward the microsecond and longer time frame, thermal processesdominate. A rule of thumb is that when the pulse width is less than 1ps, the thermal diffusion can be confined in micron dimension and HAZcan be reduced and/or even eliminated.

When ultrafast lasers are combined with high power (thermal inducedbonding) (as high as kW level) operation, both advantages of ultrafastprocess (ionization) and thermal process result in strong, high speedbonding. The ionization process helps disassemble the chemical or atomicbonds of the material being welded and re-bond through ultrafastchemical reaction to form strong stable phase structure. This process ofbond disassembly does not occur for thermal bonding. The high poweroperation further helps strengthen the bonding areas. Moreover, the highpower operation further reduces the threshold of ionization and resultsin the strong bonding of dissimilar materials.

Many parameters impact three-dimensional AM quality. In terms of laserparameters; energy, pulse width, average power, pulse repetition rate(PRR), peak power, beam quality, focal spot size, scanning speed andcontour, and mode of operation all impact the quality. In terms of AMdynamics; heat flow, chemical reaction, metal evaporation, thermaldiffusion and transfer, and stress and fatigue affect quality. In termsof metallurgy; solidification and cooling, composition, powder size andshape, grain/microstructure formation, phase transformation, cracking,and femtochemistry all influence quality. Ultrafast laser based AM is avery complicated process that involves many possible parametervariables.

FIG. 5 is a schematic illustration of an apparatus for additivemanufacturing with a high energy high power ultrafast laser, inaccordance with some embodiments.

In some embodiments, apparatus 500 comprises a high energy, high powerlaser pulse 505 generated by a high pulse repetition rate fs laser 510.In some embodiments, the laser 510 is a fiber laser. The high energy,high power laser may also be a thin disk laser or a hybrid fiberlaser/thin disk laser. The laser will have a PRR from about 0.1 MHz upto 1 GHz, an average power of about 1 to 2000 W, a pulse width of about0.1 to 1 ns, an energy from about 0.1 μJ to 30 mJ, and a wavelengthbetween about 0.2 to 3 μm. Ideally, it should have diffraction limitedbeam quality (single mode), but in practice, it can be multi-mode aswell. The small spot size allows for precise focusing of fs pulses withexcellent beam quality (nature of fiber laser) which is favorable formicro-scale AM processes. Examples of ultrafast fiber lasers include butare not limited to ytterbium (Yb) doped fiber laser at 1025-1100 nm andits harmonic generations to green and UV, erbium (Er) doped fiber laserat 1025-1610 nm and its harmonic generations, thulium (Tm) doped fiberlaser at 1950-2050 nm, holmium (Ho) doped fiber laser at 2050-2150 nm,and Er:ZBLAN fiber lasers at 2700-2900 nm. Examples of thin disk lasersinclude but are not limited to potassium gadolinium tungstate (KGW) orpotassium yttrium tungstate (KYW) based lasers (1030-1070 nm) and itsharmonic generations (green and UV). Examples of hybrid fiber laser/thindisk laser include using fs fiber laser as a seeding laser for a thindisk amplifier to obtain both high energy and high power fs lasers.

In some embodiments, a computer 515 is first used to convert an AutoCADor SolidWorks design to 3D printing procedures and contours. Theconversion may also been done on some external computing device that isnot part of the apparatus. The computer 515 is used to control the PRR,to generate a group of burst mode pulses (involve one or multiple micropulses in one macro pulses, as shown in FIG. 6), to shape grouped microand macro pulses in amplitude and temporal separation (Macro pulse PRR),to control the power of the laser 510, and to coordinate the scanner520, to control the powder delivery system, and to control the linearand rotary motorized stages 535. In some embodiments, the high energy,high power pulse 505 is coupled into an auto focusing scanner 520 whichscans and focuses the pulse 505 onto the sample 525 being manufacturedfrom the powder 530 being deposited on the stage at first and thensubsequent layers of the sample 525, resulting in a strong weld/bondbetween the sample and the powder. Beam shaping optics positionedbetween the ultrashort pulse laser and the focusing mechanism may alsobe used to modify the beam from Gaussian shape to flat top (square orround) as illustrated in FIG. 7. The sample 525, may be positioned usingits own linear and rotary motor stages 535, in X, Y, Z, Θ, and Φ. Thelinear and rotary motor stages 535 may be controlled by the computer515. An imager and processor 540, such as a CCD, may also be controlledby the computer 515. The imager and processor 540 monitors the samplesthrough a dichroic filter 545 as the sample 525 is being additivelymanufactured. The scanner 520 may be an acousto-optic type scanner(diffraction), a magnetic resonant scanner, a mechanical scanner(rotating mirror), or an electro-optic scanner, etc.

Compared with conventional CW or nanosecond laser AM techniques, thehigh energy, high power fs laser AM system of FIG. 5 creates a muchstronger micro-scale weld/bond between the sample 525 and the powder 530through ultrafast ionization, chemical reaction, and thermal bonding. Atthe beginning of the AM process, similar or dissimilar metal powders arewelded/bonded together to start the manufacture of the sample. Sample525 can be either a pre-manufactured bulk part or powder. The additivemanufacturing involves localized heating and is HAZ free since themicro-bond is accomplished by precise focusing of the ultrafast fspulses on the joining interface of the sample and the powder. Theresulting high peak intensity in the focal region ionizes the materialof the sample and the powder and creates hot plasma at the interfacewith limited to no impact on the surrounding area (i.e., HAZ free). Asthe molten pool (resulting from temperatures going to over 5,000° C.) islocalized and quickly built up only in the vicinity of the focus, thethermal stress and thermally induced cracks are largely suppressed. As aresult of the nonlinear absorption around the focal volume of the laserpulses, the high energy, high power fs laser system can achieve highlyspace-selective joining with sub-micron spatial resolution resulting ina stable sub-micron powder bonding, thus offering a higher degree ofdesign flexibility. Additionally, within an ultrashort period, thelocalized heating helps form stable phase structure and small grainsize. As an example, bonding between nickel titanium (NiTi) andstainless steel using a high energy, high power fs laser system forms astable single phase supersaturated β-Ti(Fe) structure.

In some embodiments, reduced directionality of the additivemanufacturing may be achieved by using circularly polarized high energy,high power fs laser pulses scanned quickly and rotationally (wobblefunction) in micron scale onto the joining interface between the samplebeing manufactured and the injected powder. Doing so may break thedirectionality of dendritic structures, thus making the sample robustagainst mechanical and thermal stresses in all directions.

Specifically, in micro-device AM, a microscopic lens (high NA, >0.5 forexample) may be used to create sub-micron size focal beam along beamshaping technique. The focal spot size in air for the laser beam can becalculated by 1.22*λ/N.A., where λ is the laser wavelength and N.A. isthe numerical aperture of the objective lens. The method described inU.S. Pat. No. 8,675,193 (Near-field material processing system, Mar. 18,2014) can also be used to make smaller 3D AM devices down to a fewnanometers.

FIG. 8A is a schematic illustration of a powder delivery system for anapparatus for additive manufacturing by selective laser melting with ahigh energy high power ultrafast laser and FIG. 8B is a close-up of themelting of the powder of the fabrication powder bed, in accordance withsome embodiments.

In some embodiments, powder delivery system 800 is placed onto the stage535 of FIG. 5 for AM of the sample 525. The powder delivery system 800comprises the powder 805 loaded into a powder vessel 810 placed adjacentto a receptacle 815 where the sample is fabricated. The powder vessel810 has a powder delivery piston 820 that raises the level of the powderabove the lip of the powder vessel. Next, a roller 825 moves the raisedpowder into the adjacent receptacle 815 and spreads the powder 805 intoa smooth even layer. At the beginning of the AM, the fabrication powderbed 806 is first spread over a fabrication piston 830. After this firstlayer has been melted, the fabrication piston 830 is lowered and anotherlayer of the powder 805 is uniformly spread into the fabrication powderbed 806 and over the just sintered layer for layer-by-layer fabrication.In some embodiments, at least the first layer is not sintered, thusproviding a thermal barrier between the powder layer that is firstmelted and the fabrication piston 830. In the embodiment illustrated inFIGS. 8A and 8B, the laser beam 835 selectively melts the powder whichhas been uniformly spread into the receptacle 815. The laser beam 835 isscanned in the direction 860 over the fabrication powder bed 806 andresults in melted powder particles 855. Since the temperature created bythe ultrafast laser can be over the melting temperature of the powder,the powder is completely melted. For each specific powder, the laserparameters (energy, pulse width, pulse repetition rate average power,wavelength, etc.), the scanner speed, powder size and shape, and focalspot size are optimized to generate a temperature larger than themelting temperature of the powder, but lower than the boilingtemperature of the powder. The powder 805 may comprise one or moredifferent powder materials. The one or more different powder materialsmay comprise aluminum, steel, stainless steel, titanium, and therefractory metals, niobium, molybdenum, tantalum, tungsten, and rhenium.The one or more different powders may also comprise ceramics such ashafnium (Hf) and zirconium (Zr) based diboride (HfB₂ and ZrB₂), titaniumcarbide (TiC), titanium nitride (TiN), thorium dioxide (ThO₂), siliconcarbide (SiC), tantalum carbide (TaC) and their associated composites.The one or more different powders may also comprise glasses and crystalssuch as fused silicon, BK7, quartz, diamond, grapheme, sapphire, andothers. The one or more different powders may also comprisesemiconductors such as silicon, germanium, GaAs, etc. The powder size ofthe material ranges from about 0.01 micron to 50 microns, preferablyless than 10 micron. The powder shape of the material is preferably around sphere shape. In some embodiments, the stage 535 with the powderdelivery system 800 is enclosed in a chamber 840 filled with a shieldgas 845 such as argon, helium, nitrogen, and/or hydrogen to help thesample avoid oxidation and chemical reaction or interaction with air.The ionization potentials for argon and helium are 15.7 eV and 24.5 eV.In this embodiment, the chamber has a window 850 where the laser beam835 passes through the walls of the chamber 840 and onto the fabricationpowder bed 806 in the receptacle 815. In an alternative embodiment, thechamber only substantially encloses the powder delivery system and notthe stage. In this embodiment the chamber and the powder delivery systemboth sit on the stage. The additive manufacturing may be performed ontoany size and shape substrate using the apparatus illustrated in FIG. 5,FIG. 8A, and FIG. 8B.

In an alternative embodiment, the powder vessel comprises a hopperplaced above the receptacle, wherein when the hopper is opened, theforce of gravity causes the powder to fall towards and onto thereceptacle. Between selective laser melting of a layer, the powder isdispensed from the hopper and onto the already processed layer. Afterbeing dispensed, a roller is brought into contact with the dispensedpowder and moved across the manufacturing region to spread the powderinto a smooth even layer. The layer is then ready for SLM. This processis repeated until fabrication of the sample has been completed.

FIG. 9 is an SEM of a formed shaped structure resulting from selectivelaser melting of tungsten powder, in accordance with some embodiments.

FIG. 10 is an SEM of the cross-section of the formed shaped structureresulting from selective laser melting of tungsten powder, in accordancewith some embodiments.

FIG. 11 is an EDX spectrum of a fully melted region of the formed shapedstructure resulting from selective laser melting of tungsten powder, inaccordance with some embodiments.

In some embodiments, a high energy, high power ultrafast fiber laseroperating with a 30 mJ pulse energy, a 1 MHz repetition rate, and a 1mm/s scanning speed is used to sinter a tungsten powder layer comprisedof 10 micron size tungsten powder. An argon shield gas is used duringthe sintering of the powder. FIG. 9 shows a partially melted region 905and a formed shaped structure 910 which has been completely melted. FIG.10 shows an SEM of the cross-section of the completely melted region ofthe formed shaped structure 910. A sub-micron grain as shown withinregion 1005 indicates that the 10 micron size tungsten powder hascompletely melted and been recrystallized. No voids or cracks areobserved in the cross-section of the completely melted region. Theuniform submicron grain size observed under SEM indicates that a strongbond results from using the high energy, high power ultrafast fiberlaser at high PRR. Formed shaped structures as long as 20 mm in length,width, and thickness may be manufactured using the apparatus illustratedin FIG. 5, FIG. 8A, and FIG. 8B. FIG. 11 shows an energy-dispersiveX-ray (EDX) spectrum of the completely melted region marked by dashedbox 915 of FIG. 9. The 4.6% by weight carbon (C) that was detected is aresult of the epoxy that was used for processing the sample for SEM. Nooxygen was detected in the region indicated by 915 which means that themelt was 100%.

FIG. 12 is an SEM of a ceramic wire resulting from selective lasermelting of hafnium diboride (HfB₂) powder, in accordance with someembodiments.

FIG. 13 is an SEM of the cross-section of the ceramic wire resultingfrom selective laser melting of HfB₂ powder, in accordance with someembodiments.

FIG. 14 is an SEM of the grain structure of the ceramic wire resultingfrom selective laser melting of HfB₂ powder, in accordance with someembodiments.

FIG. 15 is an EDX spectrum of a fully melted region of the ceramic wireresulting from selective laser melting of HfB₂ powder, in accordancewith some embodiments.

In some embodiments, a 1 MHz, 50 W fs fiber laser (with 20 μm spot size)is focused onto hafnium diboride powder (with a 10 micron powderdiameter size) to write a small ceramic wire with a 10 mm length and a20-50 μm width. An argon shield gas is used during the sintering of thepowder. An SEM of the wire is shown in FIG. 12. The region 1205 showsthat the ceramic wire has less than 3 μm roughness, which indicates thatthe HfB₂ powder was completely melted during the sintering. An SEM ofthe cross-section at 2,900× magnification is shown in FIG. 13. No voidsor cracks are visible in the cross-section of the ceramic wire. The SEMof the cross-section at 100,000× magnification, as shown in FIG. 14,reveals that the grain microstructure is less than 2 μm. The small grainmicrostructure is beneficial for high strength structures. An EDXspectrum of the ceramic wire is shown in FIG. 15. The EDX spectrumreveals that the ceramic wire was comprised of 81.08% by weight ofhafnium and 17.27% by weight of boron. A trace of oxygen, 1.65% byweight, was detected in the ceramic wire. The small oxygen peak resultedfrom the imperfect argon shielding during sintering. Overall, the 1 MHz,50 W fs fiber laser was capable of practically bonding an ultra-hightemperature ceramic powder into a three-dimensional additivelymanufactured structure by completely melting the HfB₂ powder into astructure with 20-50 μm feature size, which is key for the fabricationof components with tiny radii.

FIG. 16 is a block diagram illustrating a method for additivemanufacturing by selective laser melting with a high energy high powerultrafast laser, in accordance with some embodiments.

In some embodiments, processing begins at step 1605 where a high energy,high power ultrafast laser is used to generate electromagnetic radiationcomprising a high energy, high power fs laser pulse. The maincharacteristic of the ultrashort laser pulse is the high peak intensitythat results in rapid (picosecond) delivery of energy into the material,which is much faster than the plasma expansion (nanosecond tomicrosecond), thus significantly reducing or eliminating thermaldamages. In some embodiments, the high energy, high power laser pulse isgenerated by a high PRR fs laser. In other embodiments, the laser is afiber laser. The high energy, high power laser may also be a thin disklaser or a hybrid fiber laser/thin disk laser. The laser will have a PRRfrom about 0.1 MHz up to 1 GHz, an average power of about 1 to 2000 W, apulse width of about 0.1 to 1 ns, an energy from about 0.1 μJ to 30 mJ,and a wavelength between about 0.2 to 3 μm. Examples of ultrafast fiberlasers include but are not limited to Yb doped fiber laser at 1025-1100nm and its harmonic generations to green and UV, Er doped fiber laser at1025-1610 nm and its harmonic generations, Tm doped fiber laser at1950-2050 nm, Ho doped fiber laser at 2050-2150 nm, and Er:ZBLAN fiberlasers at 2700-2900 nm. Examples of thin disk lasers include but are notlimited to KGW or KYW based lasers (1030-1070 nm) and its harmonicgenerations (green and UV). At step 1610, linear and rotary motor stagesare used to position a powder delivery system within the scanning andfocus range of the high energy, high power fs laser pulse. At step 1615,one or more powders are uniformly spread into a fabrication powder bedfor selective laser melting by the high energy, high power fs laser. Atstep 1620, the high energy, high power fs laser pulse is focused andscanned onto the fabrication powder bed of the powder delivery system.The resulting high peak intensity in the focal region ionizes thematerial of the powder and creates hot plasma with limited to no impacton the surrounding area (i.e., HAZ free). As the molten pool islocalized and quickly built up only in the vicinity of the focus, thethermal stress and thermally induced cracks are largely suppressed. Insome embodiments, the high energy, high power fs laser pulse comprisescircularly polarized laser pulses which are rotationally scanned inmicron scale across the sample in order to break the directionality ofdendritic structures. The resulting weld/bond joints are more robustagainst mechanical and thermal stresses in all directions. In someembodiments, the method further comprises at step 1625 placing thelinear and rotary motor stages and powder delivery system into a chamberwith an inert gas to shield and protect the AM process from thesurrounding elements. In some embodiments, the method further comprisesat step 1630, the use of an imager and processor to monitor the sampleas the one or more powders are being bonded together by selective lasermelting to form a three-dimensional component or part.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

The benefits and advantages that may be provided by the presentinvention have been described above with regard to specific embodiments.These benefits and advantages, and any elements or limitations that maycause them to occur or to become more pronounced are not to be construedas critical, required, or essential features of any or all of theclaims. As used herein, the terms “comprises,” “comprising,” or anyother variations thereof, are intended to be interpreted asnon-exclusively including the elements or limitations which follow thoseterms. Accordingly, a system, method, or other embodiment that comprisesa set of elements is not limited to only those elements, and may includeother elements not expressly listed or inherent to the claimedembodiment.

While the present invention has been described with reference toparticular embodiments, it should be understood that the embodiments areillustrative and that the scope of the invention is not limited to theseembodiments. Many variations, modifications, additions and improvementsto the embodiments described above are possible. It is contemplated thatthese variations, modifications, additions and improvements fall withinthe scope of the invention as detailed within the following claims.

The invention claimed is:
 1. A method for three-dimensional additive manufacturing comprising: generating electromagnetic radiation from an ultrashort pulse laser, wherein the electromagnetic radiation comprises a wavelength, a pulse repetition rate, a pulse width, a pulse energy, and an average power; focusing the electromagnetic radiation into a focal region; using a powder delivery system comprising a powder vessel, a roller, and a receptacle to deposit one or more powders from the powder vessel into a receptacle at the focal region of the electromagnetic radiation and to spread the one or more powders in the receptacle into a fabrication powder bed; and using a computer to adjust the pulse repetition rate and the average power of the ultrashort pulse laser to program the electromagnetic radiation into temporally arbitrarily grouped micro and macro pulses, and to spatially shape the micro and macro pulses.
 2. The method of claim 1, wherein the powder vessel comprises a powder delivery piston configured to raise the one or more powders above the lip of the powder vessel.
 3. The method of claim 1, wherein the powder vessel comprises a hopper configured to drop the one or more powders into the receptacle.
 4. The method of claim 1, wherein the receptacle comprises a fabrication piston configured to lower the fabrication powder bed.
 5. The method of claim 1, wherein the one or more powders comprises at least one of aluminum, steel, stainless steel, titanium, niobium, molybdenum, tantalum, tungsten, rhenium, hafnium diboride, zirconium diboride, titanium carbide, titanium nitride, thorium dioxide, silicon carbide, tantalum carbide, fused silicon, BK7, quartz, diamond, graphene, sapphire, silicon, germanium, and gallium arsenide.
 6. The method of claim 1, wherein the one or more powders comprises a powder with melting temperatures greater than 2000° C.
 7. The method of claim 1, wherein the one or more powders comprises a powder with melting temperatures less than 2000° C.
 8. The method of claim 1, wherein the apparatus is configured for high resolution additive manufacturing with micron and/or sub micron level precision and/or feature size.
 9. The method of claim 1, wherein the one or more powders comprises a powder size ranging from about 0.01 μm to about 50 μm.
 10. The method of claim 1, further comprising using a chamber to substantially enclose the powder delivery system; and filling the chamber with one or more shield gases.
 11. The method of claim 10, wherein the one or more shield gases comprises at least one of argon, helium, nitrogen, and hydrogen.
 12. The method of claim 1, wherein focusing the electromagnetic radiation comprises using a scanner to receive the electromagnetic radiation from the ultrashort pulse laser and scanning within a scanning range the electromagnetic radiation onto the one or more powders to produce a sample.
 13. The method of claim 1, wherein focusing the electromagnetic radiation comprises using a microscopic lens to receive the electromagnetic radiation from the ultrashort pulse laser and focusing within a focus range the electromagnetic radiation onto the one or more powders to produce a sample, wherein the size of the sample ranges from about 0.1 μm to 20 mm.
 14. The method of claim 1, further comprising using one or more stages to support the powder delivery system and to position the powder delivery system in one or more axis within the focus range of the electromagnetic radiation.
 15. The method of claim 1, further comprising: positioning a dichroic filter between the focusing mechanism and the focal region; and focusing an imager and processor through the dichroic filter and onto a sample to monitor the sample within the focus range of the electromagnetic radiation.
 16. The method of claim 1, wherein the ultrashort pulse laser comprises at least one of a Yb doped fiber laser, an Er doped fiber laser, a Tm doped fiber laser, a Ho doped fiber laser, an Er:ZBLAN fiber laser, a KGW thin disk laser, and a KYW thin disk laser.
 17. The method of claim 1, wherein the wavelength of the electromagnetic radiation generated from the ultrashort pulse laser ranges from about 0.2 μm to 3 μm.
 18. The method of claim 1, wherein the pulse repetition rate of the electromagnetic radiation generated from the ultrashort pulse laser ranges from about 0.1 MHz to 1 GHz.
 19. The method of claim 1, wherein the pulse width of the electromagnetic radiation generated from the ultrashort pulse laser ranges from about 0.1 ps to 1 ns.
 20. The method of claim 1, wherein the pulse energy of the electromagnetic radiation generated from the ultrashort pulse laser ranges from about 0.1 μJ to 30 mJ.
 21. The method of claim 1, wherein the average power of the electromagnetic radiation generated from the ultrashort pulse laser ranges from about 1 W to 2000 W.
 22. The method of claim 1, wherein the electromagnetic radiation is polarized.
 23. The method of claim 22, wherein the electromagnetic radiation is circularly polarized.
 24. The method of claim 12, further comprising rotationally scanning on a micron scale the electromagnetic radiation onto the one or more powders.
 25. The method of claim 1, further comprising using beam shaping optics positioned at the output of the ultrashort pulse laser to modify the electromagnetic radiation from a Gaussian to a square flat top or a circular flat top.
 26. A method for three-dimensional additive manufacturing comprising: generating electromagnetic radiation from an ultrashort pulse laser, wherein the electromagnetic radiation comprises a wavelength, a pulse repetition rate, a pulse width, a pulse energy, and an average power; using beam shaping optics positioned at the output of the ultrashort pulse laser to modify the electromagnetic radiation from a Gaussian to a square flat top or a circular flat top; focusing the electromagnetic radiation into a focal region; using a powder delivery system comprising a powder vessel, a roller, and a receptacle to deposit one or more powders from the powder vessel into a receptacle at the focal region of the electromagnetic radiation and to spread the one or more powders in the receptacle into a fabrication powder bed; and using a computer to adjust the pulse repetition rate and the average power of the ultrashort pulse laser.
 27. The method of claim 26, wherein the powder vessel comprises a powder delivery piston configured to raise the one or more powders above the lip of the powder vessel.
 28. The method of claim 26, wherein the powder vessel comprises a hopper configured to drop the one or more powders into the receptacle.
 29. The method of claim 26, wherein the receptacle comprises a fabrication piston configured to lower the fabrication powder bed.
 30. The method of claim 26, wherein the one or more powders comprises at least one of aluminum, steel, stainless steel, titanium, niobium, molybdenum, tantalum, tungsten, rhenium, hafnium diboride, zirconium diboride, titanium carbide, titanium nitride, thorium dioxide, silicon carbide, tantalum carbide, fused silicon, BK7, quartz, diamond, graphene, sapphire, silicon, germanium, and gallium arsenide.
 31. The method of claim 26, wherein the one or more powders comprises a powder with melting temperatures greater than 2000° C.
 32. The method of claim 26, wherein the one or more powders comprises a powder with melting temperatures less than 2000° C.
 33. The method of claim 26, wherein the apparatus is configured for high resolution additive manufacturing with micron and/or sub micron level precision and/or feature size.
 34. The method of claim 26, wherein the one or more powders comprises a powder size ranging from about 0.01 μm to about 50 μm.
 35. The method of claim 26, further comprising using a chamber to substantially enclose the powder delivery system; and filling the chamber with one or more shield gases.
 36. The method of claim 35, wherein the one or more shield gases comprises at least one of argon, helium, nitrogen, and hydrogen.
 37. The method of claim 26, wherein focusing the electromagnetic radiation comprises using a scanner to receive the electromagnetic radiation from the ultrashort pulse laser and scanning within a scanning range the electromagnetic radiation onto the one or more powders to produce a sample.
 38. The method of claim 26, wherein focusing the electromagnetic radiation comprises using a microscopic lens to receive the electromagnetic radiation from the ultrashort pulse laser and focusing within a focus range the electromagnetic radiation onto the one or more powders to produce a sample, wherein the size of the sample ranges from about 0.1 μm to 20 mm.
 39. The method of claim 26, further comprising using one or more stages to support the powder delivery system and to position the powder delivery system in one or more axis within the focus range of the electromagnetic radiation.
 40. The method of claim 26, further comprising: positioning a dichroic filter between the focusing mechanism and the focal region; and focusing an imager and processor through the dichroic filter and onto a sample to monitor the sample within the focus range of the electromagnetic radiation.
 41. The method of claim 26, wherein the ultrashort pulse laser comprises at least one of a Yb doped fiber laser, an Er doped fiber laser, a Tm doped fiber laser, a Ho doped fiber laser, an Er:ZBLAN fiber laser, a KGW thin disk laser, and a KYW thin disk laser.
 42. The method of claim 26, wherein the wavelength of the electromagnetic radiation generated from the ultrashort pulse laser ranges from about 0.2 μm to 3 μm.
 43. The method of claim 26, wherein the pulse repetition rate of the electromagnetic radiation generated from the ultrashort pulse laser ranges from about 0.1 MHz to 1 GHz.
 44. The method of claim 26, wherein the pulse width of the electromagnetic radiation generated from the ultrashort pulse laser ranges from about 0.1 ps to 1 ns.
 45. The method of claim 26, wherein the pulse energy of the electromagnetic radiation generated from the ultrashort pulse laser ranges from about 0.1 μJ to 30 mJ.
 46. The method of claim 26, wherein the average power of the electromagnetic radiation generated from the ultrashort pulse laser ranges from about 1 W to 2000 W.
 47. The method of claim 26, wherein the electromagnetic radiation is polarized.
 48. The method of claim 47, wherein the electromagnetic radiation is circularly polarized.
 49. The method of claim 37, further comprising rotationally scanning on a micron scale the electromagnetic radiation onto the one or more powders. 